complete the given activity
. Aim: to test the presence of starch in leaf during photosynthesis
materials required :
test tube
methyl alcohol
beaker
water
bunsen burner
petri dish
iodine
*COMPLETE IT*
MUST INCLUDE:
PRECAUTIONS PROCEDURE AND CONCLUSION
Answers
Answer:
Testing a leaf for starch
Investigating photosynthesis – starch and chlorophyll
During photosynthesis a plant absorbs light energy using the pigment chlorophyll. This allows it to convert carbon dioxide and water into glucose. This glucose is:
transported to the growing parts of the plant for use in respiration
transformed into cellulose, proteins and oils
turned into starch for storage
Therefore, to test if a plant has been photosynthesising, you can test the leaf to see if starch is present.
Starch testing
Iodine solution is used to test leaves for the presence of starch. You need to:
heat a plant leaf in boiling water for 30 seconds (this kills the leaf, stopping any chemical reactions)
add the leaf to boiling ethanol in a water bath for a few minutes (the boiling ethanol dissolves the chlorophyll and removes the green colour from the leaf - it turns white so it is easy to see the change in colour)
wash with water to rehydrate and soften the leaf and spread onto a white tile
add iodine solution from a dropping pipette
After a few minutes, the parts of the leaf that contain starch turn the iodine from brown to blue/black.
Variegated leaves have green parts (where the cells contain chlorophyll) and white parts (where there is no chlorophyll). Only the parts that were green become blue/black with iodine solution, showing the importance of chlorophyll in photosynthesis. The parts without chlorophyll do not photosynthesise, and so they do not make starch and the iodine does not change colour.
Answer:
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